The present invention relates generally to apparatus and method for projecting a shape onto a scene, and more particularly to a system and method for projecting a shape onto a scene so that the shape appears to be projected via a light beam emanating from a desired source location.
There are several applications in industry that may benefit from projecting a shape into a scene (e.g., onto the surface of an object). In these applications, the intention is typically to guide a user during the performance of a task, for example, to guide a user during mechanical repair of complex systems, or to guide a user during patient set-up for radiation oncology.
In radiation oncology, a light field is typically used to represent the geometry and profile of high-energy beams that treat patients. A mirror angled at forty five degrees (45°) is positioned on a central axis of the radiation beam to bend a beam of light as if it originated from the radiation source. This method of precision alignment may achieve congruence of the light field with the radiation field. However, the method has several limitations. First, the physical characteristics of visible light are different from those of high-energy gamma rays, X-rays, or the like. For example, X-rays penetrate the beam limiting devices (e.g., jaws or maximum contaminate level (MLC) leaves), which may result in the penumbra phenomenon, where a penumbra extends the effective field beyond what is illuminated by the light field. Also, it is not possible to illuminate the scene beyond the field opening. Further, in certain situations, it may be desirable for the X-ray beam to pass through a 2-dimensional detector for entrance dosimetry. To benefit from a visible light field, such as for visual alignment, it would be necessary to move the two-dimensional detector out of the beam path, thereby adding to the design complexity of the radiation treatment device.
Consequently, it would be advantageous to provide a projection system for projecting a shape onto a scene (e.g., the surface of an object) so that the shape appears to be projected via a light beam emanating from a desired source location which may not be accessible, such as, for example, the radiation source of a radiation treatment device used in radiation oncology.